Line resonator and electron discharge device circuit therefor



Dec. 12, 1939.

LINE RESONATOR AND ELECTRON DISCHARGE DEVICE CIRCUIT T Ill O. E. DOW

Filed March 29, 1937 ////////////////////M 'lI/II II/I.

HEREFOR ATTORNEY Patented Dec. 12, 1939 UNITED STATES LINE RESONATOR AND ELECTRON DIS CHARGE DEVICE CIRCUIT THEREFOR rville E. Dow, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 29,

10 Claims.

This invention relates to tuned high frequency circuits, particularly to such of these as are known by the term concentric conductor resonator or concentric line resonator, and to elec- 6 tron discharge device circuits therefor.

By the term concentric conductor resonator or concentric line resonator is meant a tuned circuit having inner and outer, substantially concentric conductors so coupled together as to form 10 an oscillatory circuit. Examples of these are found in Reissue Patent No. 20,189, granted December 1, 1936, to Hans O. Roosenstein, also in the article Resonant lines for frequency control, by Clarence W. Hansell, published in the A. I. E. E. August, 1935, pages 852 to 857, and in copending application of James W. Conklin, Serial No. 123,096, filed January 30, 1937, to which reference is made for a more detailed description thereof.

The present invention, so far as it relates to the concentric conductor resonator, is concerned with the type wherein the inner conductor has two diameters, which is designed to reduce the overall length of the tuned circuit considerably below that of a full quarter-wave counterpart. As appears more fully in the I-Iansell article and in the copending Conklin application, supra, this double-diameter inner conductor resonator has a small diameter section which constitutes an effective inductance of minimum length necessary to attain the desired input impedance, and a larger diameter section of substantially equal length as the small diameter section, but of a diameter such as to provide a proper effective capacity for resonating at the desired frequency. The entire tuned circuit of inner and outer conductors resonates in the manner of a parallel resonance circuit in the sense that the inductive reactance of the inductive section and the capacitive reactance of the capacitive section will be formed wholly or in part by the correlative functions of the inner and outer conductors or component parts thereof. More specifically, present invention is concerned with such a double-diameter inner-conductor resonator, wherein, for reasons of compactness, the larger diameter section of inner conductor is folded back upon the smaller diameter section of inner conductor, in such manner that the overall length of line of the resonator required to tune to a given frequency is greatly reduced. This particular type of compact, folded-back, double-diameter inner-conductor resonator is described more completely in the Conklin copending application, supra.

the

1937, Serial No. 133,614

One of the objects of the present invention is to provide means for maintaining the developed length of the inner conductor of the folded-back type of double-diameter inner-conductor resonator constant, whereby there is obtained substantial freedom from the effects of variations in the ambient temperature on the resonant frequency.

A further object is toprovide a novel and desirable type of electron discharge device oscillator circuit for a concentric line resonator, wherein the resonator is coupled between the anode of the device and ground.

A still further object is to provide a constant frequency electron discharge device oscillator, wherein the grid of the device is maintained at zero radio frequency potential, and voltage from the anode is fed back to the cathode by means of a capacity potentiometer arrangement.

A feature of the invention comprises a mechanical-expanding device, dependent upon changes in temperature'and linked to one or more rods having low temperature coefficients of expansion, for compensating for the expansion and contraction of the inner conductor. Another feature employs cylinders made of materials having low temperature coefficients of expansion for compensating for the effects of temperature changes.

Other objects and features of the invention will appear from a reading of the following description which is accompanied by a drawing, wherein: Fig. 1 shows partly in cross-section and partly schematic, a folded-back concentric line reso-- nator and electron discharge device circuit in accordance with the invention; Fig. 2 illustrates a modification of the line resonator of Fig. 1.

Throughout the drawing and specification, like reference characters indicate like parts.

Fig. 1 of the drawing shows a concentric line resonator having an outer conductor l constituting a capacity member as well as the support and shielding for the entire assembly, and an inner conductor having a small diameter section 2 and .a larger diameter section 3 folded back over the small diameter section. The conductors I,

2 and 3 are, in practice, cylindrical in form, and

pedance increases and shifts phase first to a high resistance and then to equivalent capacity reactance as the length increases beyond a quarter Wave to a half wave where the reactance passes through a minimum value and changes to inductive again and repeats the process. In practice, the smaller diameter section 2 of the inner conductor (i. e. inductive section), is preferably less than oue-quarter wavelength although it might be desirable in some cases to use a longer conductor, an odd multiple of a quarter wave long. The length of section 2 would have to be between zero and one-quarter Wavelength, between a half and three-quarters wavelength, between one and one and one-quarter wavelengths, etc. The larger diameter section 3 of the inner conductor is the capacitive section, both small and large sections of inner conductor resonating at the desired frequency in the manner of a parallel resonance circuit. Inner conductor 2, 3 is conductively coupled to the outer conductor I by means of end plate I9, which supports the inner conductor and its associated adjusting equipment. At the opposite end of outer conductor I and fixed thereto by means of screws 20, 20, is the end plate I II which forms one member of an adjusting capacity comprising plate I I I and plate End plate III is removable for convenience in assembling the resonator. The small diameter section 2 of the inner conductor is mounted rigidly to the outer shell I by ring 32 and is made of a proper a length to develop the desired terminal or input impedance to the resonator. Tuning of the resonator is completed in part by capacity between the cylinder 3 and the outer conductor I. Cyilnder 3 may, if desired, be made interchangeable for accomplishing major changes and is affixed to the inner conductor through metallic plate 24 in suitable manner. The remaining tuning capacity is formed by the moving plate I3, extensible metallic bellows I4, and the end plate III. The extensible metallic bellows I4 forms a fiexible metallic connection between plate I3 and the main capacity cylinder 3. The primary connection of the capacity cylinder 3 to the inner diameter section 2 is through the plate 24. An alternative way of visualizing this type of resonator is to consider this plate 24 as the base of a section of line of which inner cylinder 2 is the inner conductor and cylinder 3 the outer conductor, and the inductive reactance thereby constituted tuned to the desired frequency by the capacity formed between cylinders I and 3 plus the capacity between plates III and I3 and the bellows capacity. The range of movement and size of the end plate I3 and bellows I4 is determined by the proportionate capacity required to be variable to cover the desired frequency range and the sensitivity of adjustment, i. e., a given capacity change could be accomplished either with a small spacing and small movement or greater spacing and greater movement. Where it is desired to cover approximately a 5% frequency range, the required sensitivity of adjustment necessitates a large range of movement. This necessitates having approximately 10% of the total capacity variable and a large diameter plate to obtain this capacity with the desired range of movement. In a particular embodiment used in practice, the frequency range was of the order of 8.2%, for which reason it was not necessary to have close spacing between plates I I I and I3, or to make the bellows I l long.

Temperature compensation is attained by providing within the small diameter section of inner conductor 2 a pair of discs 5 and 6 spaced from each other and from the section 2. A rod I of low temperature coefficient of expansion, such as Invar (a nickel-steel alloy containing about 36% nickel), is shown connected at one end (i. e. the low voltage end of the resonator) to an adjusting screw 8 and knob 9, and at the other end to disc 5 by means of a screw I0. Two other rods II and I2, located on opposite sides of the Invar rod I are also connected by screws to the upper disc 5 and also fixedly connected to the lower disc 6. Invar rod 1 is arranged to pass freely through the center of this lower disc 3. Rods II and I2 are hollow, of equal length, and made of the same material as the sections 2, 3 and outer cylinder I, preferably copper, so that they all vary in length to the same extent with changes in temperature. Also fixedly coupled to the lower disc 6 are another pair of rods I5 and I 6 of equal length and made of a low temperature coeificient of expansion material, such as Invar. Rods I5 and I6 are also fixed to the end plate I3 of the bellows M, as shown, and pass through orifices I"! and I8 in the disc 5, so as to enable relative movement between these rods and the disc 5. These last rods are, as shown, of smaller diameter than hollow rods II and I2.

In effect, we thus have an Invar rod which doubles or turns back on itself to achieve temperature compensation, as follows:

Any increase in temperature will cause an increase in the lengths of copper line sections 2 and 3. Disc 5, however, will remain fixed in position relative to end plate I9 because it is attached to the end of Invar rod I which is supported at the low voltage end of the resonator, and disc 6 will remain at a fixed distance from plate I3 since it is connected to it by Invar rods I5 and I6. Because rods H and I2 are made of copper, they will also increase in length to substantially the same degree as line sections 2 and 3. Disc 6, which is securely fastened to rods II and I2, will thus move farther away from disc 5 and cause Invar rods I5 and It, which are attached to disc t, to move with it. Inasmuch as Invar rods I5 and I6 are fastened to the end plate I3 of bellows I4, the bellows will contract in accordance with the linear expansion of the two copper rods and cylinder 2, and compensate for the changes in the length of the sections 2 and 3. A decrease in temperature will cause the same elements of the resonator to function in the reverse manner; that is, sections 2 and 3 will decrease in length, disc 6 will'move nearer disc 5, and the bellows will be caused to expand. By suitable choice of lengths of rods II and I2, among other things, the developed length of the double-diameter inner conductor 2, 3 can be kept constant irrespective of temperature variations, thus keeping the tuning of the resonator fixed.

In the simplified case of temperature compensation, rods II and I2 are made to have a length equal to that of the doubled back portion of cylinder 3. This assumes that the stray capacity of plate I3 to plate II I and cylinder 3 to plate I9 is negligible, or is independent of temperature, and that the material of rods II and I2 is the same as cylinder 3. Actually, the stray capacities mentioned do not have zero temperature coefiicient, for which reason it is necessary to increase or decrease the lengths of rods I I and I2 until a point of overall compensation is reached.

In the adjusting mechanism, a fine pitch micrometer screw 8 operates to increase or decrease the active length of Invar rod 1, thus adjusting bellows I 4 and the distance between plates 13' and l l i.

Screw 8 operates through an antifriction bearing 2i having balls 22 bearing against the base of the resonator. A coil spring 23 compressed between a flange 25 secured on the Invar erator. circuit comprising an evacuated electron discharge device 26 having a grid 27 connected to ground, a cathode 28 maintained above ground potential and its anode 29 coupled inductively to the, line resonator through lead 30. The line resonator is thus located in the anode circuit of the electron discharge device between the ground and anode and functions to control the frequency of the oscillator. In other words, the line resonator is so coupled to the electron discharge device 2% that its impedance appears between the .-a,node.29 and ground. The cathode 28 and the and the latter of the order of 1 or 2 mmf.

Since both elements of the capacity potentiometer are the same type of reactance, namely capacitive, the voltage fed back to the cathode is of the same phase as the anode voltage, a condition necessary for the production of oscillations. The radio frequency voltage on the cathode is in the same phase with the anode voltage and may be expressed by the following equation rlf Ef X w-iwhere Er is the voltage on the cathode, Ep the voltage on the anode, XCgf the capacitive reactance between grid and cathode, and XCpf the capacitive reactance between anode and cathode. One advantage of the oscillator circuit of the present invention lies in the fact .that there is eliminated the external anode circuit which is customarily necesary in cases where the concentric line is coupled between the grid and cathode of an electron discharge device.

In one embodiment of the invention, used in practice, the electron discharge device was an RCA-955 Radiotron tube of the extremely small type vknownby the trade-name Acorn, and

such device was mounted on the outer conductor 1 of the concentric resonator. The oscillator circuit and resonator functioned to produce oscillations of about 177 megacycles, although it will be appreciated that the circuit and resonator can be designed tofunction on any other desired frequency. I

It is to be distinctly understood that the concentric line resonator of the invention is not limited in its use solely to the novel type of oscillator circuit shown, but may be used wherever there is need for a tuned circuit of the concentric line resonator type.

In Fig. 1, the part of the large diameter section 3 of the inner conductor which extends out past the small diameter section 2 consists'entirely of bellows. In some designs of concentric line resonator, this need not be the case, i. e., the large diameter section 3 need not be all folded back over the small diameter section 2. Fig. 2 shows one such variation, wherein the bellows it forms only a part of the large diameter section which extends past the small diameter section 2. 'Fig. 2 shows only so much of the line resonator of Fig. l as is necessary for an understanding of this modification. Another departture of this figure from Fig. 1 is that the rods H and I2 are shown replaced with a metallic cylinder 33 which is approximately concentric with rod 1, and rods l and I6 replaced with another metallic cylinder 34 which incloses rod 1, disc 5, and cylinder 33. Disc 5, of course, is free to move within the cylinder 34, as shown.

It is also to be understood that the term ground used in the specification and appended claims is intended to mean any surface or point of zero or relatively fixed radio frequency potential.

It will be appreciated'that the invention is not limited to the precise arrangements of parts shown since various modifications may be made Without departing from the spirit and scope of the appended claims. For example, although it is shown that there are two copper rods employed in the temperature compensation feature in one embodiment of the concentric line resonator, for practical reasons, theoretically one copper rod may be used for the same purpose.

What is claimed is:

l. A concentric line resonator having an inner and an outer conductor secured together at one of their adjacent ends, said inner conductor having two hollow sections of different diameters conductively coupled together, the larger diameter section being folded back over the smaller diameter section for more than half the length of the smaller diameter section, whereby the electrical length of said line reasonator is increased Without increasing its physical length, the smaller diameter section being secured to said outer conductor at one end and to the largerdiameter section at the other end, and means within the smaller diameter section, supported at said one end, and extending over a substantial portion of the length of said smaller diameter section of inner conductor and being folded back to extend also over a substantial portion .of the length of the larger diameter section of inner conductor for maintaining the developed effective length of said inner conductor substantially constant with variations in temperature.

2. A concentric line resonator having inner and outer conductors, means mechanically coupling said conductors together at one end, said inner conductor having two sections of different diameter, a flexible conductive bellows comprising an extension of the larger diameter section of the inner conductor to vary the capacity between said larger diameter. section and said outer conductor, the smaller diameter section being supported by and directly connected to said one end, the larger diameter section being folded back over the smaller diameter section, and means within the smaller diameter section for main taining the developed effective length of inner conductor including the bellows substantially constant with variations in temperature, said means comprising a rod of very low temperature coefficient of expansion supported at one end'by said first means, another rod of very low temperature coefficient of expansion scoured at one end to said bellows and extending back for a substantial portion of the length of said first rod, and means having a predetermined temperature coefiicient of expansion linking the other ends of said rods together, whereby expansion or contraction of said last means produces an opposite movement of said bellows to compensate for changes in developed length of said inner conductor sections.

3. A concentric line resonator having inner and outer conductors mechanically coupled togather at one end, said inner conductor having two sections of different diameter, a flexible conductive bellows comprising an extension of the larger diameter section of the inner conductor to vary the capacity between said larger diameter section and said outer conductor, the smaller diameter section being supported by and directly connected to said one end, the larger diameter section being folded back over the smaller diameter section, and means within the smaller diameter section for maintaining the developed effective length of inner conductor including the bellows substantially constant with variations in temperature, said means comprising rod of very low temperature coefficient of expansion supported at one end by said mechanical coupling, a disc secured to the other end or" said rod, another rod of very low temperature coefficient of expansion secured at one end to said bellows and extending back through a hole in said disc for a portion of the length of said first rod, a disc secured to the other end of said last rod and movable with respect to said first rod, and a rod of predetermined but greater temperature coefficient of expansion than said first two rods secured to both of said discs, whereby expansion or contraction of said last rod produces an oppo-- site movement of said bellows to compensate for changes in overall length of said inner conductor sections.

4. A resonator in accordance with claim 2, characterized in this that said rods of very low temperature coefiicient of expansion are made of Invar.

5. A concentric line resonator having inner and outer copper conductors mechanically coupled together at one end, said inner conductor having two sections of difierent diameter, a fiexible conductive bellows comp-rising an extension of the larger diameter section of the inner conductor to vary the effective overall length thereof, the smaller diameter section being supported by and directly connected to said one end, the larger diameter section being folded back over the smaller diameter section, and means within the smaller diameter section for maintaining the developed eiiective length of inner conductor including the bellows substantially constant with variations in temperature, said means comprising an Invar rod supported at one end by said mechanical coupling, another Invar rod secured at one end to said bellows and extending back for a substantial portion of the length of said first Invar rod, and a copper rod linking the other ends of said rods together, whereby expansion or contraction of said copper rod produces an opposite movement of said bellows to compensate for changes in overall length of said inner conductor copper sections.

6. A concentric line resonator having inner and outer copper conductors mechanically coupled together at one end, said inner conductor having two sections of different diameter, a flexible conductive bellows comprising an extension of the larger diameter section of the inner conductor to vary the effective overall length of said larger section, the smaller diameter section being supported by and directly connected to said one end, the larger diameter section being folded back over the smaller diameter section, and means within the smaller diameter section for maintaining the developed effective length of inner conductor including the bellows substantially constant with variations in temperature, said means comprising an Invar rod supported at one end by said mechanical coupling, a disc secured to the other end of said Invar rod, a pair of parallel Invar rods of the same length located on opposite sides of said first rod and secured at one end to said bellows, said rods extending back through holes in said disc for a portion of the length of said first rod, a disc secured to the other ends of said pair of Invar rods, said last disc having a hole in the center thereof for enabling said first Invar rod to freely pass through it, and a pair of parallel copper rods of the same length secured at their ends to both of said discs, whereby expansion or contraction of said copper rods produces an opposite movement of said bellows to compensate for changes in overall length of said inner conductor sections.

7. A concentric line resonator having inner and outer conductors, means mechanically coupling said conductors together at one end, said inner conductor having two sections of different d1- ameter, a flexible conductive bellows comprising an extension of the larger diameter section of the inner conductor to vary the efiective overall length of said larger section, the smaller diameter section being supported by and directly connected to said one end, the larger diameter section being folded back over the smaller diameter section, and means within the smaller diameter section for maintaining the developed effective length of inner conductor including the bellows substantially constant with variations in temperature, said means comprising a rod of very low temperature coefficient of expansion supported at one end by said first means, a cylinder 01' very low temperature coefilcient of expansion secured at one end to said bellows and extending back for a substantial portion of said rod, and another cylinder having a predetermined coefflcient of expansion linking the other ends of said rod and first cylinder together, whereby expansion or contraction of said last cylinder produces an opposite movement of said bellows to compensate for changes in the developed length of said inner conductor sections.

8. A resonator in accordance with claim 7, characterized in this that said inner conductor sections and said last cylinder are made of the same material, said last cylinder being located within said first cylinder.

9. A concentric line resonator having inner and outer conductors, means mechanically coupling said conductors together at one end, said inner conductor having two sections of different diameter, a flexible conductive bellows comprising an extension of the larger diameter section of the inner conductor to vary the capacity between said larger diameter section and said outer conductor, the smaller diameter section being supported by and directly connected to said one end, the larger diameter section being folded back over the smaller diameter section. and means within the smaller diameter section for maintaining the developed effective length of inner conductor including the bellows substantially constant with variations in temperature, said last means extending over a substantial portion of the length of said smaller diameter section and being folded back to extend also over a substandiameter section being secured to said outer conductor at one end and to the larger diameter section at the other end, and means-supported at said one end and extending over a substantial portion of the length of said smaller diameter section of inner conductor and. being folded back to extend also over a substantial portion of the length of the larger diameter section of inner conductor for maintaining the developed efiective length of said inner conductor substantially 10 constant with variations in temperature.

ORV'IILE E. DOW. 

